With the reduction in bit size due to an increase in the recording density of a recording device, the size of a read element installed in a magnetic head has also been decreased. The read element is an element for reading out magnetic information recorded on a recording medium. In the production of the read element, it is important to control a read-core width and a read gap, which are specified by the bit size. It is also important to control an element height (MR height), which affects the element resistance, the output, the sensitivity, or the like. In order to improve the controllability of the read-core width, the read gap, and the element height, it is necessary to measure these dimensions of a produced read element and to feedback the measured values to the conditions for the production.
In recent recording devices whose recording density has been increased, the element size of the read element has been reduced. Consequently, a transmission electron microscope (TEM) having a high spatial resolution is essential for the evaluation of the shape of such an element.
In the evaluation using a TEM, an evaluation sample is processed into a thin section having a thickness of about several tens to several hundreds of nanometers. In the case where a cross-sectional sample obtained in the air bearing surface (ABS) direction is used as the evaluation sample, observation cannot be performed in the element height direction, which is orthogonal to the ABS direction. Note that the read-core width and the read gap are measured from the cross section of the sample obtained in the ABS direction.
Consequently, in a known method of evaluating an element using a TEM, two samples, namely, a cross-sectional sample obtained in the ABS direction and a cross-sectional sample obtained in the element height direction are prepared. The read-core width and the read gap are measured using the cross-sectional sample obtained in the ABS direction, and the element height is measured using the cross-sectional sample obtained in the element height direction.
However, as described above, in the known method of evaluating an element, the read-core width, the read gap, and the element height cannot be measured using a single TEM sample. Therefore, in order to measure the read-core width, the read gap, and the element height, it is necessary to prepare at least two evaluation samples. Accordingly, much labor and time have been required for the preparation of the evaluation samples.
Furthermore, because of a reduction in the element size due to an increase in the recording density, the preparation of a TEM sample for observation having the cross section obtained in the element height direction has also become difficult. More specifically, a magnetic head having an areal density of about 100 Gbpsi has an optical read-core width of about 100 nm, and it is believed that, in the near future, the optical read-core width will be reduced to 60 nm or less for an areal density of 300 Gbpsi or more. In this case, the read-core width is equal to or smaller than the thickness of a TEM sample. Accordingly, it is necessary to perform a process for producing a cross-sectional thin section with pinpoint accuracy. Therefore, it is difficult to prepare a TEM sample having a cross section at the central position of the core width (a cross section obtained in the element height direction). Accordingly, much labor and time are necessary, and the yield is also decreased.
As described above, the known technique is disadvantageous in that the read-core width, the read gap, and the element height of a read element of a magnetic head cannot be evaluated using a single sample.